Method 3015A: Microwave Assisted Acid Digestion of Aqueous

3015A - 1 Revision 1February 2007

METHOD 3015A

MICROWAVE ASSISTED ACID DIGESTION OF AQUEOUS SAMPLES AND EXTRACTS

SW-846 is not intended to be an analytical training manual. Therefore, methodprocedures are written based on the assumption that they will be performed by analysts who areformally trained in at least the basic principles of chemical analysis and in the use of the subjecttechnology.

In addition, SW-846 methods, with the exception of required method use for the analysisof method-defined parameters, are intended to be guidance methods which contain generalinformation on how to perform an analytical procedure or technique which a laboratory can useas a basic starting point for generating its own detailed Standard Operating Procedure (SOP),either for its own general use or for a specific project application. The performance dataincluded in this method are for guidance purposes only, and are not intended to be and mustnot be used as absolute QC acceptance criteria for purposes of laboratory accreditation.

1.0 SCOPE AND APPLICATION

1.1 This microwave method is designed to perform extraction using microwave heatingwith nitric acid (HNO3), or alternatively, nitric acid and hydrochloric acid (HCl). Since thismethod is not intended to accomplish total decomposition of the sample, the extracted analyteconcentrations may not reflect the total content in the sample. This method is applicable to themicrowave-assisted acid extraction/dissolution of available metals in aqueous samples, drinkingwater, mobility-procedure extracts, and wastes that contain suspended solids for the followingelements:

Element CAS Registry No. a

*Aluminum (Al) 7429-90-5

*Antimony (Sb) 7440-36-0

Arsenic (As) 7440-38-2

*Barium (Ba) 7440-39-3

*Beryllium (Be) 7440-41-7

Boron (B) 7440-42-8

Cadmium (Cd) 7440-43-9

Calcium (Ca) 7440-70-2

*Chromium (Cr) 7440-47-3

Cobalt (Co) 7440-48-4

Copper (Cu) 7440-50-8

*Iron (Fe) 7439-89-6

Element CAS Registry No. a


Lead (Pb) 7439-92-1

*Magnesium (Mg) 7439-95-4

Manganese (Mn) 7439-96-5

Mercury (Hg) 7439-97-6

Molybdenum (Mo) 7439-98-7

Nickel (Ni) 7440-02-0

Potassium (K) 7440-09-7

Selenium (Se) 7782-49-2

*Silver (Ag) 7440-22-4

Sodium (Na) 7440-23-5

Strontium (Sr) 7440-24-6

Thallium (Tl) 7440-28-0

*Vanadium (V) 7440-62-2

Zinc (Zn) 7440-66-6

a Chemical Abstract Service Registry Number

*Elements which typically require the addition of HCl for optimum recoveries. Other elements and matrices may be analyzed by this method if performance isdemonstrated for the analyte of interest, in the matrices of interest, at theconcentration levels of interest (see Sec. 9.0).

1.2 This method provides options for improving the performance for certain analytes,such as antimony, iron, aluminum, and silver by the addition of hydrochloric acid, whennecessary. It is intended to provide a rapid multi-element acid extraction prior to analysis sothat decisions can be made about materials and site clean-up levels, and as an estimate ofmetal toxicity. Digests produced by the method are suitable for analysis by inductively coupledplasma mass spectrometry (ICP-MS), inductively coupled plasma atomic emission spectrometry(ICP-AES), flame atomic absorption spectrophotometry (FLAA), and graphite furnace atomicabsorption spectrophotometry (GFAA). However, the addition of HCl may limit the quantitationmethods, or increase the difficulties of quantitation with some techniques.

Due to the rapid advances in microwave technology, consult the manufacturer'srecommended instructions for guidance on their microwave digestion system. This method isgeneric and may be implemented using a wide variety of laboratory microwave equipment.

1.3 Prior to employing this method, analysts are advised to consult the determinativemethod that may be employed in the overall analysis for additional information on quality controlprocedures, development of QC acceptance criteria, calculations, and general guidance. Analysts also should consult the disclaimer statement at the front of the manual and theinformation in Chapter Two for guidance on the intended flexibility in the choice of methods,apparatus, materials, reagents, and supplies, and on the responsibilities of the analyst for


demonstrating that the techniques employed are appropriate for the analytes of interest, in thematrix of interest, and at the levels of concern.

In addition, analysts and data users are advised that, except where explicitly specified in aregulation, the use of SW-846 methods is not mandatory in response to Federal testingrequirements. The information contained in this method is provided by EPA as guidance to beused by the analyst and the regulated community in making judgments necessary to generateresults that meet the data quality objectives for the intended application.

1.4 Use of this method is restricted to use by, or under supervision of, properlyexperienced and trained personnel. Each analyst must demonstrate the ability to generateacceptable results with this method.

2.0 SUMMARY OF METHOD

A representative aqueous sample is extracted with concentrated nitric acid or, optionally, concentrated nitric acid and concentrated hydrochloric acid, using microwave heating with asuitable laboratory microwave unit. The sample and acid(s) are placed in a fluorocarbonpolymer (such as PFA or TFM) or quartz microwave vessel or vessel liner. The vessel is sealedand heated in the microwave unit for a specified period of time. After cooling, the vesselcontents are filtered, centrifuged, or allowed to settle and then diluted to volume and analyzedby the appropriate determinative method.

3.0 DEFINITIONS

Refer to Chapter One, Chapter Three, and the manufacturer's instructions for definitionsthat may be relevant to this procedure.

4.0 INTERFERENCES

4.1 Solvents, reagents, glassware, and other sample processing hardware may yieldartifacts and/or interferences to sample analysis. All these materials must be demonstrated tobe free from interferences under the conditions of the analysis by analyzing method blanks. Specific selection of reagents and purification of solvents by distillation in all-glass systems maybe necessary. Refer to each method for specific guidance on quality control procedures and toChapter Three for general guidance on the cleaning of glassware. Also refer to thedeterminative methods to be used for a discussion of interferences.

4.2 Digestion of samples which contain organics will create high pressures due to theevolution of gaseous digestion products. This may cause venting of the vessels with potentialloss of sample components and/or analytes. When warranted by the potential reactivity of thesample, a smaller sample size may be used, and the concentration for final calculationsadjusted, but a final water volume prior to addition of acid(s) of 45 mL is recommended. Avolume of 45 mL is recommended in order to retain the heat characteristics of the calibrationprocedure (if used). Variations of the method, due to very reactive materials, are specificallyaddressed in Sec. 11.3.3. Limits of quantitation will change with sample quantity (dilution) andwith instrumentation.

4.3 Many samples can be dissolved by this method. However, when the samplecontains suspended solids which are made up of refractory compounds, such as silicon dioxide,


titanium dioxide, alumina, and other oxides, they will not be dissolved and in some cases maysequester target analyte elements. These bound elements are considered nonmobile in theenvironment and are excluded from most aqueous pollutant transport mechanisms.

4.4 Samples that are highly reactive or contaminated may require dilution beforeanalysis. If samples are diluted, then any dilutions must be accounted for in all subsequent calculations. Highly reactive samples may also require pre-digestion in a hood to minimize thedanger of thermal runaway and excessively vigorous reactions.

5.0 SAFETY

5.1 This method does not address all safety issues associated with its use. Thelaboratory is responsible for maintaining a safe work environment and a current awareness fileof OSHA regulations regarding the safe handling of the chemicals listed in this method. Areference file of material safety data sheets (MSDSs) should be available to all personnelinvolved in these analyses.

5.2 The microwave unit cavity must be corrosion resistant and well ventilated. Allelectronics must be well protected against corrosion for safe operation.

CAUTION: There are many safety and operational recommendations specific to the model andmanufacturer of the microwave equipment used in individual laboratories. A listingof these specific suggestions is beyond the scope of this method. The analyst isadvised to consult the equipment manual, the equipment manufacturer, and otherappropriate literature for proper and safe operation of the microwave equipmentand vessels. For further details and a review of safety methods during microwavesample preparation, see Ref. 4 and the documents listed in Sec. 13.3.

5.3 This method requires microwave transparent and reagent resistant materials suchas fluorocarbon polymers (examples are PFA and TFM) or quartz to contain acids and samples.For higher pressure capabilities, the vessel may be contained within layers of differentmicrowave transparent materials for strength, durability, and safety. The internal volume of thevessel should be at least 100 mL, and the vessel must be capable of withstanding pressures ofat least 30 atm (435 psi), and capable of controlled pressure relief. These specifications are toprovide an appropriate, safe, and durable reaction vessel of which there are many adequatedesigns by many suppliers.

WARNING: The outer layers of vessels are frequently not as acid or reagent resistant as theliner material. In order to retain the specified performance and safetyrequirements, these outer layers must not be chemically degraded or physicallydamaged. Routine examination of the vessel materials is necessary to ensuretheir safe use.

WARNING: Another safety concern relates to the use of sealed containers without pressurerelief devices. Temperature is the important variable controlling the reaction. Pressure is needed to attain elevated temperatures, but must be safely contained. Some digestion vessels constructed from certain fluorocarbons may crack, burst,or explode in the unit under certain pressures. Only vessels approved by themanufacturer of the microwave system being used are considered acceptable.

CAUTION: An aqueous sample must contain no more than 1% (V/V or g/V) oxidizable organicmaterial. Upon oxidation, organic material, whether liquid or solid, contributes to


gaseous digestion products. Pressure build-up above the pressure limit will resultin venting of the closed digestion vessel.

WARNING: When acids such as nitric and hydrochloric are used to effect sample digestion inmicrowave units in open or sealed vessel(s), there is the potential for acid vaporsreleased to corrode the safety devices that prevent the microwave magnetron fromshutting off when the door is opened. This can result in operator exposure tomicrowave energy. Use of a laboratory-grade microwave equipment system withisolated and corrosion resistant instrument components and safety devicesprevents this from occurring. Users are therefore advised not to use domestic(kitchen) type microwave ovens or sealed containers which are not equipped withcontrolled pressure relief mechanisms for microwave acid digestions by thismethod. Use of laboratory-grade microwave equipment is needed to preventsafety hazards. For further details, see Ref. 4 and the documents listed in Sec.13.3.

6.0 EQUIPMENT AND SUPPLIES

The mention of trade names or commercial products in this manual is for illustrativepurposes only, and does not constitute an EPA endorsement or exclusive recommendation foruse. The products and instrument settings cited in SW-846 methods represent those productsand settings used during method development or subsequently evaluated by the Agency. Glassware, reagents, supplies, equipment, and settings other than those listed in this manualmay be employed provided that method performance appropriate for the intended applicationhas been demonstrated and documented.

This section does not list common laboratory glassware (e.g., beakers and flasks).

6.1 Microwave apparatus requirements

6.1.1 The temperature performance requirements necessitate the microwavedecomposition system to sense the temperature to within ± 2.5 EC and automaticallyadjust the microwave field output power within 2 seconds of sensing. Temperaturesensors should be accurate to ± 2 EC (including the final reaction temperature of 170 ± 5EC). Temperature feedback control provides the primary performance mechanism for themethod. Due to the variability in sample matrix types and microwave digestion equipment(i.e., different vessel types and microwave oven designs), temperature feedback control ispreferred for reproducible microwave heating. For further details, consult the documentlisted in Sec. 13.3.4.

Alternatively, for a specific vessel type, specific set of reagent(s), and sample type,a calibration control mechanism can be developed similar to those described in previousmicrowave methods (see Method 3051). Through calibration of the microwave power for aspecific number and type of vessel, vessel load, and heat loss characteristics of a specificvessel series, the reaction temperature profile described in Sec. 11.3.5 can be reproduced(see document listed in Sec. 13.3.4). The calibration settings are specific for the numberand type of vessel and microwave system being used, in addition to the specific reagentcombination being used. Therefore, no specific calibration settings are provided in thismethod. These settings may be developed by using temperature monitoring equipmentfor each specific set of microwave equipment and vessel type. They may be used asdescribed in Methods 3052 and 3051. In this circumstance, the microwave systemprovides programmable power, which can be programmed to within ± 12 W of the required


power. Typical systems provide 600 W - 1200 W of power. Calibration control providesbackward compatibility with older laboratory microwave systems which may not beequipped for temperature monitoring or feedback control and with lower cost microwavesystems for some repetitive analyses. Older vessels with lower pressure capabilities maynot be compatible (see Refs. 2, 3, and 4 and the documents listed in Secs. 13.3.3 and13.3.4).

6.1.2 The accuracy of the temperature measurement system should beperiodically validated at an elevated temperature. This can be done using a container ofsilicon oil (a high temperature oil) and an external, calibrated temperature measurementsystem. The oil should be adequately stirred to ensure a homogeneous temperature, andboth the microwave temperature sensor and the external temperature sensor placed intothe oil. After heating the oil to a constant temperature of 170 ± 5 EC, the temperatureshould be measured using both sensors. If the measured temperatures vary by more than1 to 2 EC, the microwave temperature measurement system should be calibrated. Consult the microwave manufacturer’s instructions about the specific temperature sensorcalibration procedure (see Method 3052).

6.1.3 A rotating turntable is employed to ensure the homogeneous distributionof microwave radiation within the unit. The speed of the turntable should be a minimum of3 rpm. Other types of equipment that are used to assist in achieving uniformity of themicrowave field may also be appropriate.

6.2 Class A or appropriate mechanical pipette, volumetric flask, or graduated cylinder,50- or 100-mL capacity or equivalent.

6.3 Filter paper, qualitative or equivalent.

6.4 Filter funnel, glass, polypropylene, or other appropriate material.

6.5 Analytical balance, of appropriate capacity and resolution, meeting data qualityobjectives.

7.0 REAGENTS AND STANDARDS

7.1 Reagent-grade chemicals must be used in all tests. Unless otherwise indicated, itis intended that all reagents conform to the specifications of the Committee on AnalyticalReagents of the American Chemical Society, where such specifications are available. Othergrades may be used, provided it is first ascertained that the reagent is of sufficiently high purityto permit its use without lessening the accuracy of the determination.

7.2 All acids should be sub-boiling distilled and/or high purity where possible tominimize blank levels due to metallic contamination. Other grades may be used, provided it isfirst ascertained that the reagent is of sufficient purity to permit its use without decreasing theaccuracy of the determination. If the purity of a reagent is questionable, the reagent should beanalyzed to determine the level of impurities. The reagent blank must be less than the lowerlimit of quantitation in order to be used.

7.2.1 Concentrated nitric acid (HNO3) -- The acid should be analyzed todetermine levels of impurity. If the method blank is less than the lower limit of quantitation,the acid can be used.


7.2.2 Concentrated hydrochloric acid (HCl) -- The acid should be analyzed todetermine levels of impurity. If the method blank is less than the lower limit of quantitation,the acid can be used.

7.3 Reagent water -- Reagent water must be interference free. All references to waterin the method refer to reagent water unless otherwise specified. For further details, consult thedocument listed in Sec. 13.3.1.

8.0 SAMPLE COLLECTION, PRESERVATION, AND STORAGE

8.1 See the introductory material in Chapter Three, "Inorganic Analytes."

8.2 All sample containers must be prewashed with acids, water, and metal-freedetergents, if necessary, depending on the use history of the container (see the document listedin Sec. 13.3.4). Plastic and glass containers are both suitable. For further information, seeChapter Three.

8.3 Aqueous waste waters must be acidified to a pH < 2 with HNO3.

9.0 QUALITY CONTROL

9.1 Refer to Chapter One for additional guidance on quality assurance (QA) andquality control (QC) protocols. When inconsistencies exist between QC guidelines, method-specific QC criteria take precedence over both technique-specific criteria and those criteriagiven in Chapter One, and technique-specific QC criteria take precedence over the criteria inChapter One. Any effort involving the collection of analytical data should include developmentof a structured and systematic planning document, such as a Quality Assurance Project Plan(QAPP) or a Sampling and Analysis Plan (SAP), which translates project objectives andspecifications into directions for those that will implement the project and assess the results. Each laboratory should maintain a formal quality assurance program. The laboratory shouldalso maintain records to document the quality of the data generated. All data sheets and qualitycontrol data should be maintained for reference or inspection.

9.2 Initial demonstration of proficiency

Each laboratory must demonstrate initial proficiency with each sample preparation anddeterminative method combination it utilizes by generating data of acceptable accuracy andprecision for target analytes in a clean reference matrix. This will include a combination of thesample extraction method and the determinative method (a 6000 or 7000 series method). Thelaboratory must also repeat the demonstration of proficiency whenever new staff are trained orsignificant changes in instrumentation are made.

9.2.1 Prepare the reference samples from a spiking solution containing eachanalyte of interest. The reference sample concentrate (spiking solution) may be preparedfrom pure standard materials, or purchased as certified solutions. If prepared by thelaboratory, the reference sample concentrate should be made using stock standardsprepared independently from those used for calibration.

9.2.2 The procedure for preparation of the reference sample concentrate isdependent upon the method being evaluated. Guidance for reference sampleconcentrations for certain methods is listed in Sec. 9.2.4. In other cases, the


determinative methods may contain guidance on preparing the reference sampleconcentrate and the reference sample. In the absence of any other guidance, consultSec. 9.3.3 and prepare the spiking solution accordingly.

The concentration of target analytes in the reference sample may be adjusted tomore accurately reflect the concentrations that will be analyzed by the laboratory. If theconcentration of an analyte is being evaluated relative to a regulatory limit or action level,see Sec. 9.3.3 for information on selecting an appropriate spiking level.

9.2.3 To evaluate the performance of the total analytical process, the referencesamples must be handled in exactly the same manner as actual samples. See the note inSec. 9.3.1 for important information regarding spiking samples.

9.2.4 Preparation of reference samples for specific determinative methods

The following sections provide guidance on the QC reference sample concentratesfor many determinative methods. The concentration of the target analytes in the QCreference sample for the methods listed below may need to be adjusted to moreaccurately reflect the concentrations of interest in different samples or projects. If theconcentration of an analyte is being evaluated relative to a regulatory limit or action level,see Sec. 9.3.3 for information on selecting an appropriate spiking level. In addition, theanalyst may vary the concentration of the spiking solution and the volume of solutionspiked into the sample. However, because of concerns about the effects of the spikingsolution solvent on the sample, the total volume spiked into a sample should generally beheld to no more than 1 mL. For any determinative method not listed below, the analystshould consult Sec. 9.3.3 and is free to choose analytes and spiking concentrationsappropriate for the intended application. See the note in Sec. 9.3.1 for importantinformation regarding spiking samples.

NOTE: All of the concentrations listed below refer to the concentration of the spikingsolution itself, not the concentration of the spiked sample.

9.2.4.1 Method 6010, Inorganic Elements by ICP-AES -- The QCreference sample concentrate should contain each analyte at 1,000 mg/L inreagent water with appropriate type(s) and volume(s) of acid(s). See Method6010.

9.2.4.2 Method 6020, Inorganic Elements by ICP-MS -- The QCreference sample concentrate should contain each analyte at 1,000 mg/L inreagent water with appropriate type(s) and volume(s) of acid(s). See Method6020.

9.2.4.2 Method 7000, Inorganic Elements by Flame AAS -- The QCreference sample concentrate should contain each analyte at 1,000 mg/L inreagent water with appropriate type(s) and volume(s) of acid(s). See Method7000.

9.2.4.3 Method 7010, Inorganic Elements by Graphite Furnace AAS --The QC reference sample concentrate should contain each analyte at 1,000 mg/Lin reagent water with appropriat type(s) and volume(s) of acid(s). See Method7010.


9.2.4.4 Method 7061, Arsenic by AA, Gaseous Hydride -- The QCreference sample concentrate should contain arsenic at 1,000 mg/L in reagentwater with appropriate volume of concentrated nitric acid. See Method 7061.

9.2.4.5 Method 7062, Antimony and Arsenic by AA, BorohydrideReduction -- The QC reference sample concentrate should contain each analyte at1,000 mg/L in reagent water with appropriate volume of concentrated nitric acid. See Method 7062.

9.2.4.5 Method 7063, Arsenic by ASV -- The QC reference sampleconcentrate should contain mercury at 1,000 mg/L in reagent water withappropriate volume of concentrated nitric acid. Stock solutions are commerciallyavailable as spectrophotometric standards. See Method 7063.

9.2.4.6 Method 7470, Mercury in Liquid Waste by Manual Cold-VaporTechnique -- The QC reference sample concentrate should contain mercury at1,000 mg/L in reagent water with appropriate volume of concentrated nitric acid. Stock solutions are also commercially available as spectrophotometric standards. See Method 7470.

9.2.4.7 Method 7471, Mercury in Solid or Semisolid Waste by ManualCold-Vapor Technique -- The QC reference sample concentrate should containmercury at 1,000 mg/L in reagent water with appropriate volume of concentratednitric acid. Stock solutions are also commercially available as spectrophotometricstandards. See Method 7471.

9.2.4.8 Method 7472, Mercury by ASV -- The QC reference sampleconcentrate should contain mercury at 1,000 mg/L in reagent water withappropriate volume of concentrated nitric acid. Stock solutions are alsocommercially available as spectrophotometric standards. See Method 7472.

9.2.4.9 Method 7473, Mercury by Thermal, Decomposition, Amalgamation, and AA -- The QC reference sample concentrate should contain mercury at 1,000 mg/L in reagent water with appropriate volume of concentratednitric acid. Stock solutions are also commercially available as spectrophotometricstandards. See Method 7473.

9.2.4.10 Method 7474, Mercury by Atomic Fluorescence -- The QCreference sample concentrate should contain mercury at 1,000 mg/L in reagentwater with appropriate volume of concentrated nitric acid. Stock solutions are alsocommercially available as spectrophotometric standards. See Method 7474.

9.2.4.11 Method 7741, Selenium by AA, Gaseous Reduction -- The QCreference sample concentrate should contain selenium at 1,000 mg/L in reagentwater. See Method 7741.

9.2.4.12 Method 7742, Selenium by AA, Borohydride Reduction -- TheQC reference sample concentrate should contain selenium at 1,000 mg/L inreagent water. See Method 7742.

9.2.5 Analyze at least four replicate aliquots of the well-mixed referencesamples by the same procedures used to analyze actual samples. This will include acombination of the sample preparation method and the determinative method (a 6000 or


7000 series method). Follow the guidance on data calculation and interpretationpresented in the determintive method.

9.3 Sample quality control for preparation and analysis

9.3.1 Documenting the effect of the matrix should include the analysis of atleast one matrix spike and one duplicate unspiked sample or one matrix spike/matrix spikeduplicate pair per analytical batch. The decision on whether to prepare and analyzeduplicate samples or a matrix spike/matrix spike duplicate must be based on a knowledgeof the samples in the sample batch. If samples are expected to contain target analytes,laboratories may use one matrix spike and a duplicate analysis of an unspiked fieldsample. If samples are not expected to contain target analytes, then laboratories shoulduse a matrix spike and matrix spike duplicate pair. The consideration as to which samplefor a given batch is selected for QC analyses should be decided during the projectplanning process and documented in an approved sampling and analysis plan. The actualsample selected for QC analyses should be representative of the entire matrix compositionfor a given extraction batch, since data quality assumptions will likely be applied to allbatch samples based on compliance to the stated data quality objectives and meeting therecommended precision and accuracy criteria. Therefore, it is inappropriate to combinedissimilar matrices in a single sample preparatory batch and expect to use a single set ofQC samples. Sec. 9.3.3 provides guidance on establishing the concentration of the matrixspike compounds in the sample chosen for spiking.

The choice of analytes to be spiked should reflect the analytes of interest for thespecific project. Thus, if only a subset of the list of target analytes provided in adeterminative method are of interest, then these would be the analytes of interest for theproject. In the absence of project-specific analytes of interest, it is suggested that thelaboratory periodically change the analytes that are spiked with the goal of obtainingmatrix spike data for most, if not all, of the analytes in a given determinative method. Ifthese compounds are not target analytes for a specific project, or if other compounds areknown to be of greater concern at a given site, then other matrix spike compounds shouldbe employed.

CAUTION: The utility of the data for the matrix spike compounds depends on the degreeto which the spiked compounds mimic the compounds already present in afield sample. Therefore, it is CRITICAL that any compounds added to asample are added to the sample aliquot PRIOR TO any additional processingsteps. It is also CRITICAL that the spiked compounds be in the samechemical form as the target compounds.

9.3.2 A laboratory control sample (LCS) should be included with each analyticalbatch. The LCS consists of an aliquot of a clean (control) matrix similar to the samplematrix and of the same weight or volume: e.g., reagent water for the water matrix or sandor soil for the solid matrix. The LCS is spiked with the same analytes at the sameconcentrations as the matrix spike, when appropriate. When the results of the matrixspike analysis indicate a potential problem due to the sample matrix itself, the LCS resultsare used to verify that the laboratory can perform the analysis in a clean matrix.

9.3.3 The concentration of the matrix spike sample and/or the LCS should bedetermined as described in the following sections.

9.3.3.1 If, as in compliance monitoring, the concentration of a specificanalyte in the sample is being checked against a regulatory limit or action level, the


spike should be at or below the regulatory limit or action level, or 1 - 5 times thebackground concentration (if historical data are available), whichever concentrationis higher.

9.3.3.2 If historical data are not available, it is suggested that anuncontaminated sample of the same matrix from the site be submitted for matrixspiking purposes to ensure that high concentrations of target analytes and/orinterferences will not prevent calculation of recoveries.

9.3.3.3 If the concentration of a specific analyte in a sample is notbeing checked against a limit specific to that analyte, then the concentration of thematrix spike should be at the same concentration as the reference sample (Sec.9.2.4), near the middle of calibration range, or approximately 10 times thequantitation limit in the matrix of interest. It is again suggested that a backgroundsample of the same matrix from the site be submitted as a sample for matrixspiking purposes.

9.3.4 Analyze these QC samples (the LCS and the matrix spikes or the optionalmatrix duplicates) following the procedures in the determinative method. Calculate andevaluate the QC data as outlined in the determinative method.

9.3.5 Blanks -- The preparation and analysis of method blanks and other blanksare necessary to track potential contamination of samples during the extraction andanalysis processes. Refer to Chapter One for specific quality control procedures.

9.4 The laboratory must also have procedures for documenting the effect of the matrixon method performance. Refer to Chapter One and each determinative method for specificguidance on developing method performance data.

9.5 Periodically, the accuracy of the temperature measurement system used to controlthe microwave equipment should be validated per Sec. 6.1.2.

9.6 (This step is not necessary if using temperature feedback control.) Each day thatsamples are extracted, the microwave-power calibration should be verified by heating 1 kg ofASTM Type II water (at 22 ± 3 EC) in a covered, microwave-transparent vessel for 2 min at thesetting for 490 W and measuring the water temperature after heating per Sec. 10.5. If thepower calculated (according to Sec. 12.0) differs from 490 W by more than ± 10 W, themicrowave settings should be recalibrated according to Sec. 10.0.

9.7 The choice of an acid or acid mixture for digestion will depend on the analytes ofinterest and no single acid or acid mixture is universally applicable to all analyte groups. Whatever acid or acid mixture is employed, including those specifically listed in this method, theanalyst must demonstrate adequate performance for the analytes of interest, at the levels ofinterest. At a minimum, such a demonstration will encompass the initial demonstration ofproficiency described in Method 3500, using a clean reference matrix. Method 8000 describesprocedures that may be used to develop performance criteria for such demonstrations as wellas for matrix spike and laboratory control sample results.


10.0 CALIBRATION AND STANDARDIZATION

The following sections provide information regarding the calibration of microwaveequipment.

NOTE: If the microwave unit uses temperature feedback control to control the performancespecifications of the method, then performing the calibration procedure is notnecessary.

10.1 Calibration is the normalization and reproduction of a microwave fieldstrength to permit reagent and energy coupling in a predictable and reproducible manner. It balances reagent heating and heat loss from the vessels and is equipment dependentdue to the heat retention and loss characteristics of the specific vessel. Available power isevaluated to permit the microwave field output in watts to be transferred from onemicrowave system to another.

Use of calibration to control this reaction requires balancing output power, coupledenergy, and heat loss to reproduce the temperature heating profile given in Sec. 11.3.5. The conditions for each acid mixture and each batch containing the same specifiednumber of vessels must be determined individually. Only identical acid mixtures andvessel models and specified numbers of vessels may be used in a given batch.

10.2 For cavity type microwave equipment, calibration is accomplished bymeasuring the temperature rise in 1 kg of water exposed to microwave radiation for a fixedperiod of time. The analyst can relate power (in watts) to the partial power setting of thesystem. The calibration format needed for laboratory microwave systems depends on thetype of electronic system used by the manufacturer to provide partial microwave power. Few systems have an accurate and precise linear relationship between percent powersettings and absorbed power. Where linear circuits have been utilized, the calibrationcurve can be determined by a three-point calibration method (see Sec. 10.4). Otherwise,the analyst must use the multiple point calibration method (see Sec. 10.3). Assistance incalibration and software guidance of calibration are available in Ref. 4 and the documentlisted in Sec. 13.3.4.

10.3 Multiple-point calibration involves the measurement of absorbed powerover a large range of power settings. Typically, for a 600 W unit, the following powersettings are measured: 100, 99, 98, 97, 95, 90, 80, 70, 60, 50, and 40% using theprocedure described in Sec. 10.5. These data are clustered about the customary workingpower ranges. Non-linearity has been encountered at the upper end of the calibration. Non-linearity is primarily encountered when using older instrumentation, however, multi-point calibration is recommended for use with all instrumentation when accurate andprecise temperature feedback control is not available. If the system's electronics areknown to have nonlinear deviations in any region of proportional power control, it will benecessary to make a set of measurements that bracket the power to be used. The finalcalibration point should be at the partial power setting that will be used in the test. Thissetting should be checked periodically to evaluate the integrity of the calibration. If asignificant change is detected (± 10 W), then the entire calibration should be re-evaluated.

10.4 The three-point calibration involves the measurement of absorbed powerat three different power settings. Power is measured at 100% and 50% using theprocedure described in Sec. 10.5. From this 2-point line, determine the partial powersetting that corresponds to the power, in watts, specified in the procedure to reproduce theheating profile specified in Sec. 11.3.6. Measure the absorbed power at that partial power


setting. If the measured absorbed power does not correspond to the specified powerwithin ± 10 W, use the multiple-point calibration in Sec. 10.3. This point should also beused to periodically verify the integrity of the calibration.

10.5 Equilibrate a large volume of water to room temperature (22 ± 3 EC). Onekg of reagent water is weighed (1,000.0 ± 0.1 g) into a fluorocarbon beaker or a beakermade of some other material that does not significantly absorb microwave energy (glassabsorbs microwave energy and is not recommended). The initial temperature of the watershould be 22 ± 3 EC measured to ± 0.05 EC. The covered beaker is circulatedcontinuously (in the normal sample path) through the microwave field for 2 min at thedesired partial power setting with the system's exhaust fan on maximum (as it will beduring normal operation). The beaker is removed and the water is vigorously stirred. Usea magnetic stirring bar inserted immediately after microwave irradiation (irradiating with thestir bar in the vessel could cause electrical arcing) and record the maximum temperaturewithin the first 30 seconds to ± 0.05 EC. Use a new sample for each additionalmeasurement. If the water is reused (after making adjustments for any loss of weight dueto heating), both the water and the beaker must have returned to 22 ± 3 EC. Threemeasurements at each power setting should be made.

The absorbed power is determined by the following relationship:

P'(K)(Cp)(m)(∆T)

t

Where:

P = the apparent power absorbed by the sample in watts (W) (joule sec-1)

K = the conversion factor for thermochemical calories sec-1 to watts (K= 4.184)

Cp = the heat capacity, thermal capacity, or specific heat (cal g-1 EC-1) of water

m = the mass of the water sample in grams (g)

∆T = the final temperature minus the initial temperature (EC)

t = the time in seconds (s)

Using the experimental conditions of 2 min (120 sec) and 1 kg (1000 g) of distilledwater (heat capacity at 25 EC is 0.9997 cal g-1 EC-1), the calibration equation simplifies to:

P ' ∆T 34.86

NOTE: Stable line voltage is necessary for accurate and reproducible calibration andoperation. The line voltage should be within manufacturer's specification. During measurement and operation the line voltage should not vary by morethan ± 2 V (see the document listed in Sec. 13.3.4). Electronic components inmost microwave units are matched to the system's function and output. When


any part of the high voltage circuit, power source, or control components in thesystem have been serviced or replaced, it will be necessary to recheck thesystem’s calibration. If the power output has changed significantly (± 10 W),then the entire calibration should be re-evaluated.

11.0 PROCEDURE

11.1 Temperature control of closed vessel microwave instruments provides the mainfeedback control performance mechanism for the method. Method control requires atemperature sensor in one or more vessels during the entire digestion. The microwavedecomposition system should sense the temperature to within ± 2.5 EC and permit adjustmentof the microwave output power within 2 seconds.

11.2 All digestion vessels and volumetric ware must be carefully acid washed andrinsed with reagent water. When switching between highly concentrated samples and lowconcentrated samples, all digestion vessels (fluoropolymer or quartz liners) should be cleanedby leaching with hot (greater than 80 EC, but less than boiling) hydrochloric acid (1:1) for aminimum of two hours followed by hot (greater than 80 EC, but less than boiling) nitric acid (1:1)for a minimum of two hours. The vessels should then be rinsed with reagent water and dried ina clean environment. This cleaning procedure should also be used whenever the prior use ofthe digestion vessels is unknown or cross contamination from prior sample digestions in vesselsis suspected. Polymeric or glass volumetric ware and storage containers should be cleaned byleaching with more dilute acids (approximately 10% V/V) appropriate for the specific materialused and then rinsed with reagent water and dried in a clean environment.

11.3 Sample digestion

11.3.1 Measure a 45 mL aliquot of a well-shaken, homogenized sample using anappropriate volumetric measurement and delivery device, and quantitatively transfer thealiquot to an appropriate vessel equipped with a controlled pressure relief mechanism. Samples that are highly reactive or contaminated may require dilution. If samples arediluted, then any dilutions must be accounted for in all subsequent calculations

11.3.2 Add 5 ± 0.1 mL of concentrated nitric acid or, alternatively, 4 ± 0.1 mL ofconcentrated nitric acid and 1 ± 0.1 mL of concentrated hydrochloric acid to the vessel in afume hood (or fume exhausted enclosure). The addition of concentrated hydrochloric acidto the nitric acid is appropriate for the stabilization of certain analytes, such as Ag, Ba, andSb and high concentrations of Fe and Al in solution. Improvements and optimalrecoveries of Sb and Ag upon addition of HCl have been described in the literature (seethe document listed in Sec. 13.3.4). The addition of hydrochloric acid may, however, limitthe quantitation techniques or increase the difficulties of analysis for some quantitationsystems.

WARNING: The addition of hydrochloric acid must be in the form of concentratedhydrochloric acid and not from a premixed combination of acids. A build-upof chlorine gas, as well as other gases, will result from a premixed acidsolution. These gases may be violently released upon heating. This isavoided by adding the acid in the described manner.

WARNING: Toxic nitrogen oxide(s) and chlorine fumes are usually produced duringdigestion. Therefore, all steps involving open or the opening of microwavevessels must be performed in a properly operating fume ventilation system.


WARNING: The analyst should wear protective gloves and face protection.

CAUTION: The use of microwave equipment with temperature feedback control isneeded to control any unfamiliar reactions that may occur during the leachingof samples of unknown composition. The leaching of these samples mayrequire additional vessel requirements such as increased pressurecapabilities.

11.3.3 The analyst should be aware of the potential for a vigorous reaction,especially with samples containing suspended solids of easily oxidized organic species. When digesting a matrix of this type, a vigorous reaction upon the addition of reagent(s)may present a safety hazard. Do not leach this type of sample as described in thismethod, due to the high potential for unsafe and uncontrollable reactions. Instead, thesesamples may be predigested in a hood, with the vessel loosely capped to allow gases toescape, eliminating the hazard presented by rapid addition of thermal energy (MW power)to a reactive mixture. After predigestion, the samples may be digested according to theprocedures described in this method.

11.3.4 Seal the vessel according to the manufacturer's directions. Properlyplace the vessel in the microwave system according to the manufacturer's recommendedspecifications and, when applicable, connect appropriate temperature and pressuremonitoring equipment to vessels according to manufacturer’s specifications.

11.3.5 This method is a performance-based method, designed to achieve orapproach consistent leaching of the sample through achieving specific reaction conditions. The temperature of each sample should rise to 170 ± 5 EC in approximately 10 min andremain at 170 ± 5 EC for 10 min, or for the remainder of the 20-min digestion period (seeRefs 1, 2, and 3 and the document listed in Sec. 13.3.4). Figure 1 shows the time vs.temperature and pressure profiles for the leaching of three simulated wastewater samplesusing this method (these data are presented for guidance purposes only). The samplesare composed of approximately 0.35 g SRM 2704 (Buffalo River Sediment) mixed in 45mL of double-deionized water. The figure demonstrates the temperature and pressureprofiles for both the all-nitric digest (5 mL of concentrated nitric acid), and the nitric andhydrochloric mixed-acid digest (4 mL of concentrated nitric acid and 1 mL of concentratedhydrochloric acid). Also shown is the profile for the heating of the wastewater samplewithout addition of acids. When using temperature feedback control, the number ofsamples that may be simultaneously digested may vary, from one sample up to themaximum number of vessels that can be heated by the magnetron of the microwave unitaccording to the heating profile specified in this section. The number will depend on thepower of the unit, the number of vessels, and the heat loss characteristics of the vessels(see the document listed in Sec. 13.3.4).

11.3.5.1 Calibration control is applicable in reproducing this methodprovided the power in watts versus time parameters are determined to reproducethe specifications listed in Sec. 11.3.5. The calibration settings will be specific tothe quantity of reagents, the number of vessels, and the heat loss characteristics ofthe vessels (see the document listed in Sec. 13.3.4). If calibration control is beingused, any vessels containing acids for analytical blank purposes are counted assample vessels. When fewer than the recommended number of samples are to bedigested, the remaining vessels should be filled with 45 mL of water, and the acidmixture added, so that the full complement of vessels is achieved. This providesan energy balance, since the microwave power absorbed is proportional to the totalabsorbing mass in the cavity (see the document listed in Sec. 13.3.4). Irradiate


each group of vessels using the predetermined calibration settings. (Differentvessel types should not be mixed.)

11.3.6 At the end of the microwave program, allow the vessels to cool for aminimum of 5 min before removing them from the microwave system. Cooling of thevessels may be accelerated by internal or external cooling devices. When the vesselshave cooled to near room temperature, determine if the microwave vessels havemaintained their seal throughout the digestion. Due to the wide variability of vesseldesigns, a single procedure is not appropriate. For vessels that are sealed as discreteseparate entities, the vessel weight may be taken before and after digestion to evaluateseal integrity. If the weight loss of the sample exceeds 1% of the weight of the sampleand reagents, then the sample is considered compromised. For vessels with burst disks,a careful visual inspection of the disk, in addition to weighing, may identify compromisedvessels. For vessels with resealing pressure relief mechanisms, an auditory or a physicalsign that can indicate whether a vessel has vented is appropriate.

11.3.7 Complete the preparation of the sample by venting microwave containersin a fume hood before uncapping, so as to avoid a rush of acid vapor that may still be inthe headspace. When sufficiently cool to handle, carefully uncap the vessels, using theprocedure recommended by the vessel manufacturer. Quantitatively transfer the sampleto an acid-cleaned bottle. If the digested sample contains particulates which may clognebulizers or interfere with injection of the sample into the instrument, the sample may becentrifuged (Sec. 11.3.7.1), allowed to settle (Sec. 11.3.7.2), or filtered (Sec. 11.3.7.3).

11.3.7.1 Centrifugation: Centrifugation at 2,000 - 3,000 rpm for 10 minis usually sufficient to clear the supernatant.

11.3.7.2 Settling: If undissolved material, such as SiO2, TiO2, or otherrefractory oxides, remains, allow the sample to stand until the supernatant is clear. Allowing a sample to stand overnight will usually accomplish this. If it does not,centrifuge or filter the sample.

11.3.7.3 Filtering: If necessary, the filtering apparatus must bethoroughly cleaned and prerinsed with dilute (approximately 10% V/V) nitric acid. Filter the sample through qualitative filter paper into a second acid-cleanedcontainer.

11.3.8 The removal or reduction of the quantity of sample may be desirable forconcentration of analytes prior to analysis. The chemistry and volatility of the analytes ofinterest should be considered and evaluated when using this alternative (see Ref. 4 andthe document listed in Sec. 13.3.4). Sample evaporation in a controlled environment withcontrolled purge gas and neutralizing and collection of exhaust interactions is analternative where appropriate. This manipulation may be performed in the microwavesystem, if the system is capable of this function, or external to the microwave system inmore common apparatus. This option must be tested and validated to determine analyteretention and loss and should be accompanied by equipment validation possibly using thestandard addition method and standard reference materials. For further information, seeRef. 4, the document listed in Sec. 13.3.4, and Method 3052.

NOTE: The final solution typically requires nitric acid to maintain appropriate samplesolution acidity and stability of the elements. Commonly, a 2% (v/v) nitric acidconcentration is desirable. Waste minimization techniques should be used to


capture reagent fumes. This procedure should be tested and validated in theapparatus and on standards before using on unknown samples.

11.3.9 Transfer or decant the sample into volumetric ware and dilute the digestto a known volume. The digest is now ready for analysis for elements of interest usingappropriate elemental analysis techniques.

12.0 DATA ANALYSIS AND CALCULATIONS

12.1 Calculations: The concentrations determined are to be reported on the basis of theactual volume of the original sample. All dilutions must be taken into account when computingthe final results.

12.2 Prior to using this method, verify that the temperature sensing equipment isproperly reading temperature. A procedure for verification is given in Sec. 6.1.2. This willestablish the accuracy and precision of the temperature sensing equipment, which should becarried throughout the statistical treatment of the quality assurance data.

12.3 In calibrating the microwave unit (Sec. 10.0), the power absorbed (for each powersetting) by 1 kg of reagent water exposed to 120 sec of microwave energy is determined by thefollowing expression:

Power (in watts) = (T1 - T2) (34.86)

Where:

T1 = Initial temperature of water (between 21 and 25 EC to nearest 0.1 EC)

T2 = Final temperature of water (to nearest 0.1 EC)

12.4 Plot the power settings against the absorbed power (calculated in Sec. 12.3) toobtain a calibration relationship. Alternatively, use a microwave calibration program to analyzethe calibration data (see Ref. 4 and the document listed in Sec. 13.3.4). Interpolate the data toobtain the instrument settings needed to provide the wattage levels specified in Sec. 12.3.

13.0 METHOD PERFORMANCE

13.1 Performance data and related information are provided in SW-846 methods only asexamples and guidance. The data do not represent required performance goals for users of themethods. Instead, performance goals should be developed on a project-specific basis, and thelaboratory should establish in-house QC performance criteria for the application of this method.These performance data are not intended to be and must not be used as absolute QCacceptance criteria for purposes of laboratory accreditation.

13.2 The fundamental analytical validation of this method with nitric acid has beenperformed (Ref. 3). The results are shown in Tables 1a and 1b for guidance purposes only. Variations of this method including nitric acid and hydrochloric acid have also been published inthe literature (see the documents listed in Secs. 13.3.3 and 13.3.4). The method has also beentested on a variety of matrices, including two simulated wastewater matrices, one consisting of


~ 0.35 g sediment (SRM 2704) mixed with 45 mL of double-deionized water, and the otherconsisting of ~ 0.35 g of soil (SRM 4355) mixed with 45 mL of double-deionized water. Theresults are shown in Tables 2 and 3. These data are presented for guidance purposes only.

13.3 The following documents may provide additional guidance and insight on thismethod and technique:

13.3.1 1985 Annual Book of ASTM Standards, Vol. 11.01; "StandardSpecification for Reagent Water," ASTM, Philadelphia, PA, 1985, D1193-77.

13.3.2 Introduction to Microwave Sample Preparation: Theory and Practice

(Chapters 6 and 11), Kingston, H. M. and Jassie, L. B., Eds., ACS Professional ReferenceBook Series, American Chemical Society, Washington, DC, 1988.

13.3.3 H. M. Kingston and P. J. Walter, "Comparison of Microwave VersusConventional Dissolution for Environmental Applications," Spectroscopy, Vol. 7 No. 9, 20-27, 1992.

13.3.4 H. M. Kingston, S. J. Haswell, Eds, "Environmental Microwave SamplePreparation: Fundamentals, Methods, and Applications," in Microwave EnhancedChemistry: Fundamentals, Sample Preparation, and Applications, ACS ProfessionalReference Book Series, American Chemical Society, Washington, DC 1997.

14.0 POLLUTION PREVENTION

14.1 Pollution prevention encompasses any technique that reduces or eliminates thequantity or toxicity of waste at the point of generation. Numerous opportunities for pollutionprevention exist in laboratory operations. The EPA has established a preferred hierarchy ofenvironmental management techniques that places pollution prevention as the managementoption of first choice. Whenever feasible, laboratory personnel should use pollution preventiontechniques to address their waste generation. When wastes cannot be feasibly reduced at thesource, the Agency recommends recycling as the next best option.

14.2 For information about pollution prevention that may be applicable to laboratoriesand research institutions, consult Less is Better: Laboratory Chemical Management for WasteReduction, available from the American Chemical Society's Department of GovernmentRelations and Science Policy, 1155 16th Street, NW, Washington, DC 20036,http://www.acs.org.

15.0 WASTE MANAGEMENT

The Environmental Protection Agency requires that laboratory waste managementpractices be conducted consistent with all applicable rules and regulations. The Agency urgeslaboratories to protect the air, water, and land by minimizing and controlling all releases fromhoods and bench operations, complying with the letter and spirit of any sewer discharge permitsand regulations, and by complying with all solid and hazardous waste regulations, particularlythe hazardous waste identification rules and land disposal restrictions. For further informationon waste management, consult The Waste Management Manual for Laboratory Personnelavailable from the American Chemical Society at the address listed in Sec. 14.2.


16.0 REFERENCES

1. H. M. Kingston, Final Report EPA IAG #DWI3932541-01-I, September 30, 1988, AppendixA. 2. M. Shannon, Alternate Test Procedure Application, USEPA Region V, Central Regional

Laboratory, 536 S. Clark Street, Chicago, IL 60606, 1989.

3. P. Sosinski, and C. Sze, "Absolute Accuracy Study, Microwave Digestion Method 3015(nitric acid only);" EPA Region III Central Regional Laboratory, 1991.

4. Duquesne University, Analytical Sample Preparation and Microwave Chemistry Center. SamplePrep Web, http://www.sampleprep.duq.edu/

5. D. D. Link, H. M. Kingston, P. J. Walter, "Development and Validation of the New EPAMicrowave-Assisted Leach Methods 3051A and 3015A."

17.0 TABLES, DIAGRAMS, FLOWCHARTS, AND VALIDATION DATA

The following pages contain the tables and figure referenced by this method.


TABLE 1a

RECOVERY OF ANALYTES IN CERTIFIED REFERENCE MATERIAL WATER SAMPLES BYICP-OES AFTER DIGESTION BY METHOD 3015 (NITRIC ONLY): RESULTS OF

VALIDATION STUDY (REF. 3)

TM-11a TM-12a T-95b T-107b T-109b

Element Mean ± StdDev

CertMean

Mean± StdDev

CertMean

Mean± StdDev

CertMean

Mean± StdDev

CertMean

Mean± StdDev

CertMean

Al 480 ± 26

510 2800 ±88

2687 210 ± 19

220 120 ± 31

113

As 13 ± 1 10.8 90 ± 11 81.5

Ba 140 ± 23

450 2400 ±70

2529 200 ± 16

192

Be 11.3 ± 0.5

11.0 26 ± 26 22.1

Ca 12000± 783

11700 59000± 999

35400

Cd 45 ± 2 40.8 240 ± 8

237 12 ± 1 14.3 10 ± 2 12.1

Co 240 ± 14

227 1150 ±36

1067

Cr 64 ± 4 52.1 350 ± 10

299 23 ± 23 13 30 ± 6 18.7

Cu 78 ± 4 46.3 320 ± 9

288 42 ± 42 30 34 ± 4 21.4

Fe 290 ± 16

249 1180 ±43

1089 60 ± 9 52 130 ± 7

106

K 5000 ±784

4700 2600 ± 383

2330

Mg 35000± 1922

32800 2200 ± 110

2100 10200± 218

9310

Mn 61 ± 3 46.0 300 ± 9

1089 53 ± 53 45 47 ± 3 34

Na 20000±

10690

190000 2300 ± 1056

20700 13800± 516

12000264

Ni 280 ± 16

1290 ±39

1234 61 ± 2 57

Pb 280 ± 32

275 1360 ±35

1326 30.1 ± 0.2

26 39 ± 1 34.9

Se 65.97 ±2.65

60.1 13 ± 13 11

V 530 ± 26

491 2400 ±61

2319

Zn 56 ± 3 55.4 520 ± 9

314 31 ± 3 75.8 70 ± 4 74

a Semi-synthetic, aqueous certified reference material from Research and Applications Branch,National Water Research Institute, Canada Centre for Inland Waters, Reference Materials -Waterb USGS standard reference water sample


TABLE 1b

RECOVERY OF ANALYTES IN EPA WATER ANALYSIS PERFORMANCE EVALUATION SAMPLES BY ICP-OES AFTER DIGESTION BY METHOD 3015 (NITRIC ONLY): RESULTS

OF VALIDATION STUDY (REF. 3)

WP980 #1c WP980 #2c WS378 #12c

Element Mean ±Std Dev

Cert Mean

Mean ±Std Dev

Cert Mean

Mean ±Std Dev

Cert Mean

Sb 18.0 ± 0.5 16.92 110 ± 34 101.5

Tl 55 ± 2 50 7.0 ± 0.5 6.26

Ag 19 ± 5 46

c EPA water analysis performance evaluation samples, water pollution (WP) and water supply(WS) series.


TABLE 2

EXAMPLE COMPARISON OF ANALYTE RECOVERIES FROM “SIMULATED WASTEWATER”MIXTURE OF ~ 0.35 G SRM 2704 (BUFFALO RIVER SEDIMENT)

AND 45 ML DOUBLE-DEIONIZED WATER, USING BOTH DIGEST OPTIONS (REF. 5)

Element 5 mL HNO3 digest

4 mL HNO3 + 1 mL HCl digest

Total AnalyteConcentration

Ag 0.31 ± 0.05 0.41 ± 0.09 ---*B 23.8 ± 3.1 30.6 ± 8.3 ---*

Be 0.81 ± 0.13 0.91 ± 0.19 ---*Co 12.0 ± 0.30 11.5 ± 0.98 14.0 ± 0.6Hg ---- 1.49 ± 0.03 1.44 ± 0.07Mo 2.97 ± 0.72 3.15 ± 0.28 ---*Ni 39.6 ± 2.5 41.3 ± 1.7 44.1 ± 3.0Sr 41.9 ± 1.3 49.0 ± 1.6 (130)V 6.18 ± 2.5 14.6 ± 2.4 95 ± 4Zn 418 ± 12 412 ± 31 438 ± 12

Results reported in µg/g analyte (mean ± 95% confidence limit).Total concentrations are taken from NIST SRM Certificate of Analysis.Values in parenthesis are reference concentrations.Quantitative determinations made using Flame AA or ICPMS.* The total concentration of this analyte in SRM 2704 is not certified.


TABLE 3

EXAMPLE COMPARISON OF ANALYTE RECOVERIES FROM “SIMULATED WASTEWATER”MIXTURE OF ~0.35 G SRM 4355 (PERUVIAN SOIL) AND

45 ML DOUBLE-DEIONIZED WATER, USING BOTH DIGEST OPTIONS (REF. 5)

Element 5 mL HNO3 digest

4 mL HNO3 + 1 mL HCl digest

Total AnalyteConcentration

Ag 1.31 ± 0.12 1.62 ± 0.11 (1.9)*B 32.9 ± 2.1 31.8 ± 2.7 (63)*

Co 10.5 ± 0.34 10.4 ± 0.41 14.8 ± 0.76Mo 0.99 ± 0.06 1.1 ± 0.11 (1.7)*Ni 12.2 ± 1.2 13.1 ± 1.9 (13)*Pb 135 ± 4 136 ± 4 129 ± 26Sb 3.7 ± 0.30 5.2 ± 0.53 14.3 ± 2.2Sr 140 ± 6 143 ± 7 (330)

Results reported in µg/g analyte (mean ± 95% confidence limit).Total concentrations are taken from NIST SRM Certificate of Analysis.Quantitative determinations made using Flame AA or ICPMS* Values in parenthesis are reference concentrations.


FIGURE 1

THE TYPICAL TEMPERATURE AND PRESSURE PROFILE FOR THE HEATING OF A SIMULATED WASTEWATER SAMPLE (~ 0.35 G OF SRM 2704 + 45 ML OF DOUBLE-

DEIONIZED WATER) USING BOTH DIGEST OPTIONS (5 ML OF HNO3 AND 4 ML OF HNO3 + 1 ML OF HCL)


11.3.7.1 - 11.3.7.3Centrifuge, settle or

filter sample.

10.1 Calibrate microwave equipment. *

11.3.2 Add 5 ±0.1 mL conc. HNO3 or,alternatively, 4±0.1 mL conc. HNO3

and 1±0.1 mL conc. HCl.

11.3.1 Measure 45 mL aliquot ofsample into the digestion vessel.

11.2 Acid wash and water rinse alldigestion vessels and glassware.

11.3.3 Hasvigorous

reaction takenplace?

11.3.3 Sample may represent asafety hazard. Pre-digest sample

in a hood, with vessel looselycapped to allow gases to escape,

before proceeding.

11.3.7 Transfer sample toacid-cleaned bottle.

11.3.5 Heat samples accordingto time vs pressure profiles.

11.3.4 Seal and place vessels inmicrowave system.

11.3.6 Allow vessels to cool toroom temperature.

Have vesselsmaintainedtheir seal?

11.3.8 Remove or reduce quantity ofsample by evaporation with controlled

purge gas.

Are particulatespresent?

12.0 Calculate concentrationsbased on original sample volume.

Start

Stop

Yes

No

YesNo

Yes

No

* Not necessary if using a unit equipped with temperature feedback control.

METHOD 3015A

MICROWAVE ASSISTED ACID DIGESTION OF AQUEOUS SAMPLES AND EXTRACTS

Documents

Method 3015A: Microwave Assisted Acid Digestion of Aqueous